Satellite TV & Linux Geostationary Satellites ● We want the satellite to stand still ● But the earth is rotating at 1 revolution per 24H ● So we want the satellite to move with us ● Some physics: GmM/r^2=mw^2r → r=36,000 Km (earth radius is only 6,000 Km) ● All satellites are located above the equator, which is South of Israel ● positions are longitude e.g. 13E, 4W, 7W etc ... Satellites Dish ● A dish, is a hyperbolic shaped reflector (mirror), concentrating incoming radio waves at it's focus ● This is similar to taking a magnifying glass and focusing the Sun's light at a spot ● An LNB (low noise block) is located at the dish's focus ● Prime vs. offset dish LNB - Low Noise Block ● The LNB is comprised of: ● Dipole antenna – The actual antenna ● Low Noise Amplifier – Amplify the signal before “catching” noise is from the electronics. ● Frequency Down conversion – Convert to Frequencies that can be transferred via coax without being attenuated too much ● Quad LNB. Monoblock LNB, multiple LNBS Diseqc – Digital Satellite Equipment Control ● Diseqc 1.0 – connects to 4 LNBs ● Diseqc 1.1 – connects to 4 Diseqc 1.0 ● Diseqc 1.2 & 1.3 – mobile dish ● Diseqc 2.x – same as 1.x but bidirectional Transponder Required information: Frequency Symbol Rate (SR) Polarization FEC (can be set to auto) May have many channels Statistical Multiplexing Feeds Encryption / Conditional access ● CSA (Common Scrambling Algorithm) ● CAM (Conditional access module) ● FTA (Free To Air) ● Smart Card DVB-S Vs. DVB-S2 ● DVB-S: QPSK (4PSK), TRELLIS, MPEG2 ● DVB-S2: 8PSK, LDPC, H-264. introduced to support HD. (though HD is possible via DVB-S) ● DVB-T, DVB-H, ATSC etc ... Due to ”political issue” DVB-S2 development was forked and stalled. There were many half baked branches. ● About 6 months ago, there was a decision to create a new API: S2API. It was merged into kernel 2.6.28 Israel's Upcoming DVB-T ● AFAIK: ● H264 – not supported by regular DVBT STB ● Channels: 1,2,10,33,99 ● Channels 9 & 23 not included (politics ?) ● Will indoor antenna suffice ? ● Probably commence on July 2009 Software ● Drivers – depends on adapter, may be built in into kernel. There is also a loopback device. ● VDR – as close as can be to a real STB. ● MYTHTV – full blown HTPC. Distributed. ● Kaffeine – KDE app ● Cmdline – use your favorite media player via /dev/dvb VDR VDR Myth - Main Myth – Watch TV Myth – Watch TV Myth – Weather Myth – Program Guide Mythweb - Listings Mythweb - Schedule Software ● VDR – as close as can be to a real STB. can be used with soft-device. Has many plug-ins. (but no Hebrew subtitles AFAIK). ● MYTHTV – full blown HTPC. Distributed, Harder to install... ● Kaffeine – KDE app ● Cmdline – use your favorite media player ● Both myth/vdr can record multiple channels on same transponder Linux Based STB ● There are a few Linux Based receivers on the market. ● Dreambox is the popular choice – popular enough to be a target for copies ... ● Features like time shifting. (modules without a hard-drive requires an external NFS server) ● Some software images supports only original Dreamboxes (there are rumors about bricking the non originals). ● Original and alternate firmwares EPG – Electronic Program Guide Some channels have On-line EPG TV_GRAB_* : Perl based scripts, which downloads EPG from different Internet sites, and converts them to an XMLTV format tv_grab_dvb – may be used for cross source eit. Websites www.lyngsat.com - info: sat, freq, chans, etc... www.dvbsupport.net/freetv.html - free TV פורום הלווינים הישראלי - www.sat-israel.com www.mythtv.org - mythtv www.cadsoft.de/vdr - vdr http://dvbn.happysat.org/viewforum.php?f=17 - Linux specific sat forum, discussions on many issues, HD (VDPAU), patches to vdr/myth/kaffeine, etc ... Hardware issues NVIDIA Vs. ATI NVIDIA's VDPAU (Video Decode and Presentation API for Unix) offload portions of the video decoding/post-processing to the GPU. SS2 (DVB-S), S2-3600 (USB. Problems ?), FULL HD interlaced Before you buy PC Hardware: GPU (VDPAU, 8400gs vs. newer, vc1), DVB-Card (Budget/FF), display, lirc. STB (FTA only ?) Which satellites (num, size, and mobility of dishes. Num LNBs). Is South (SE/SW) blocked ? How many TVs Modulation: PSK (Just for general knowledge) ● A Sine wave is 90 90 transmitted, its phase holds the information ● 4PSK (QPSK) – 90 4 options (2 bits/sym): 45,135,225,315 180 0 ● 8PSK – 270 8 options (3 bits/sym): 0,45,90,135,180,225, 270,315 QPSK / 4PSK / QAM-4 Error correction (Just for general knowledge) ● Convolution code. Aka Trellis: Not all sequences of data are valid, choose the ”path” that is most probable. ● LDPC – low density parity check. For Each group of data bits, a sum is calculate. Each bit is a member of more than one group. In case of contradiction between bits and sum, the error can be corrected using other sums. Satellite TV & Linux The End.